1. Field of the Invention
The present invention relates to a developing apparatus and an image forming apparatus, and more specifically a mechanism for supplying a developer.
2. Description of the Related Art
In typical image forming apparatuses, such as photocopiers, facsimiles, printers, or printing presses, an electrostatic latent image carried on a photosensitive element as a latent-image carrying member is developed with a toner included in a developer through image-visualization processing.
Toner that did not contribute to the image-visualization processing is discarded to a waste container, or returned to a developing apparatus for recycling.
As a developer, a two-component developer that contains a toner and a carrier, and a one-component developer that contains only a toner are known.
A toner to be used in the image-visualization processing needs to be electrically charged so that it electrostatically adheres onto a latent image. To electrically charge the toner, in the case of the two-component developer, there is a method of stirring mixing the two-component developer with a stirring roller. On the other hand, in the case of the one-component developer, there is method of stirring and rubbing the one-component developer while a layer thickness is regulated by a doctor blade for controlling the layer thickness, when toner is carried on the developer carrying member, such as a developing sleeve.
However, if stirring and rubbing are repeated, a mechanical load strongly acts on the toner in the developer, as a result, problems occur as described below.
In the case of a one-component developer, silica or titan, of which particles are to be fluidizing particles, is outwardly added to a toner resin; however, these substances are sometimes stripped or go into hiding inside the toner resin. As a result, fluidity expected to be provided by the fluidizing particles cannot be secured whereby the developer easily sticks on the surface of a member that carries the developer, and causes toner filming that stuck toner is deposited and forms a thin layer, resulting in inferior development due to poor developing bias.
Moreover, mechanical load repeatedly acts on the layer-thickness regulating member against which toner repeatedly collides, thereby causing wear and resulting that accurate regulation of the layer thickness cannot be performed, and bringing about abnormality in an image on a part when deteriorated toner is adhered on the part.
On the other hand, in the case of a two-component developer, the developer adheres to a magnetic carrier, forms a magnetic brush, and repeatedly receives mechanical stress during stirring mixing, thereby resulting in problems that coating on toner particles is stripped and an adverse effect appears on charging performance, and that mechanical stress becomes large due to the use of a magnetic carrier of which mass is larger than the toner, and leads to deterioration in the developer.
As a method of conveying toner without applying mechanical stress to the toner, a method of using air-flow conveyance (for example, see Japanese Patent Publication No. 3920845), and a method of electrostatically conveying toner (for example, see Japanese Patent Application Laid-open No. 2006-17695) are proposed.
Moreover, as a method of electrically charging a toner without applying mechanical stress to the toner, a method of charging via a dielectric process during electrostatic conveyance (for example, see Japanese Patent Application Laid-open No. 2004-280068), and a method of charging by using an electric-field forming unit on the way of a conveying channel for toner (for example, see Japanese Patent Application Laid-open No. 2005-221631) are proposed.
Japanese Patent Publication No. 3920845 discloses a configuration that includes an air-flow conveying unit that includes an outlet in opposition to a magnetic brush to be formed on a developer carrying member is provided, and a charging unit is arranged inside a flow channel of toner used by the air-flow conveying unit.
Japanese Patent Application Laid-open No. 2006-17695 discloses a configuration that includes a bias unit for electrostatically conveying toner inside air bubble that is to be a passage for toner, and charging of toner is performed by using an occasion when toner being electrostatically conveyed contacts with air-bubble inner surface.
Japanese Patent Application Laid-open No. 2004-280068 discloses a configuration that includes an electrostatic conveying unit arranged in a conveying channel of toner to be conveyed toward a developer carrying member, and friction charge of toner is performed when the toner moves while contacting the electrostatic conveying unit.
Japanese Patent Application Laid-open No. 2005-221631 discloses a configuration that includes a one-axis screw pump, and friction charge can be performed when toner moves through a passage inside the screw pump.
One of the above documents discloses a configuration that generates mechanical stress onto a toner, such as stirring mixing, or layer-thickness regulation. Moreover, the toner can be charged on the way of conveyance.
However, according to any of the above configurations, charging of toner is performed during a conveying process of the toner. When such a configuration adapted, charged toner moves while contacting the conveying channel and a conveying member in a conveying process until being delivered to the developer carrying member, so that a fear that outward additive of toner may be stripped is not completely solved.
It is assumed that friction charge is performed while toner is moving through the conveying channel, therefore, a certain length of the conveying channel appropriate to charge is required, and it cannot be expected to reduce the size of the apparatus due to the length of the conveying channel. There is concern that the cost of parts may increase, because a larger electrode is required for electrostatic conveyance for a longer conveying channel. Furthermore, there is concern that a configuration relevant to toner conveyance becomes more complicated, because in order to convey toner electrostatically, a number of electrodes having different polarities need to be arranged in parallel, and bias control is required with respect to each electrode.